Desiccant

ESD Handbook TR 20.20 paragraph 5.4.3.2.2 Temperature “While only specialized materials and structures can control the interior temperature of a package, it is important to take possible temperature exposure into account when shipping electronic parts. It is particularly important to consider what happens to the interior of a package if the environment has high humidity. If the temperature varies across the dew point of the established interior environment of the package, condensation may occur. The interior of a package should either contain desiccant or the air should be evacuated from the package during the sealing process. The package itself should have a low WVTR (Water Vapor Transfer Rate).”

Note: A desiccant is a substance, such as calcium oxide or silica gel, that has a high affinity for water and is used as a drying agent.